Implicit styling inside a container

I want to apply Padding="0"

to everyone Label

on the left sidebar (the first one StackPanel

) so that it is left aligned with each TextBox

(and other controls).

How can I define an implicit style in <ApplicationResources>

that only applies to elements in a particular container?

Alternative:

• Use x:Key="sidebarLabel"
  
  . However, this setting seems overkill for many sidebar shortcuts in my actual application.
• Add Padding=0
  
  to each Label
  
  in the sidebar. This is essentially the same as the previous alternative.
• Move the implicit style to <StackPanel.Resources>
  
  . However, I want the styles (in App.xaml
  
  ) to be separate from the XAML (in MainWindow.xaml
  
  ).

<Application.Resources>
    <Style TargetType="{x:Type Label}">
        <Setter Property="Padding" Value="0" />
    </Style>
</Application.Resources>      

      

        
        
        
      

    

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="2*"/>
    </Grid.ColumnDefinitions>

    <StackPanel Grid.Column="0">
        <GroupBox Header="New User">
            <StackPanel>
                <Label>First Name:</Label>
                <TextBox/>
                <Label>Last Name:</Label>
                <TextBox/>
            </StackPanel>
        </GroupBox>
    </StackPanel>
    <GroupBox Grid.Column="1" Header="Main">
        <StackPanel>
            <Label>I want default padding here</Label>
        </StackPanel>
    </GroupBox>
</Grid>